1. Far Detector Timing Calibration Andy Blake Cambridge University November 2004

2. Motivation (1) (Calibration Status June 2004) hardware changes Upward-going PC analysis is extremely unforgiving on timing calibration! Need to understand timing well – motivation for an alternative calibration.

3. Motivation (2) (Data/MC status June 2004) Timing resolution: Data = 2.75 ns MC = 2.40 ns RMS down for stopping muons: … try to understand this discrepancy …

4. Calibration Procedure HARDWARE CHANGES TIMEWALK CORRECTIONS CALIBRATION CONSTANTS (iterate) DATABASE RAW DATA Use straight muons (~400-500 hits/strip-end/month)

5. Refractive Index Intrinsically tied up with timewalk effects! Use standard calibration + set high pulseheight threshold. Extract effective n from CT east - CT west vs. fibre east - fibre west. tails off at n ~ 1.77

6. (1) Hardware Changes Look for sudden changes in east-west time difference. Resolve east-west ambiguity by looking at mean residuals for independent timing fits on east and west sides. > 200 timing jumps identified at chip level. EAST WEST EAST - WEST

7. Bad Electronics SPURIOUS DISPLACED TIMESTAMPS

8. Bad PMT

9. (2) Timewalk Corrections Fit timing along muon track using strip ends > 5000 ADCs. Calculate mean timing residuals for strip ends < 5000 ADCs. timing effects from rise of dynode signal not modelled

10. (3) Calibration [ input corrections for hardware changes + timewalk ] Calibrate the electronics. –Do east / west calibration independently. –Calibrate offsets between PMTs within each VARC using muons that pass through the entire VARC. –Calibrate offsets between VARCs using muons that pass through two entire VARCs. –Use T east - T west to measure overall east/west time difference. Calibrate the strip ends. –Electronics should now be flat! –Calculate offsets between strip-ends using all muons. Validate Calibration using EAST minus WEST timing.

11. Results (1) test sample r18000-19500 (~2 months data)

12. Results (2) hardware changes cause tails

13. Results (3) Applying appropriate corrections to data/MC for hardware changes, timewalk + calibration: RMS data ~ 2.45 ns RMS MC ~ 2.30 ns preliminary

14. Conclusion Able to remove the effects of hardware changes and to apply corrections for timewalk. Timing calibration tested at strip level. (Currently calibrating all data from 8/03 – 11/04) Data and MC agree better than ever before! (But still need to do some fine-tuning) Need to study calibration drift – how often do constants need to be recalculated? Upward-going analysis about to be kick-started!